1. Field of the Invention
The present invention relates to a vibration damping device to be used, for example, for an automobile engine mount, especially to a fluid filled vibration damping device using vibration effects based on the flow behavior of a non-compressible fluid sealed therein.
2. Description of the Related Art
Conventionally, as a vibration damping device interposed between the members constituting a vibration transmission system that connects said members to each other or supports them in a vibration-damping manner, there has been known a fluid filled vibration damping device using the flow behavior of a non-compressible fluid sealed therein, which is widely used as an engine mount and the like. This fluid filled vibration damping device has a structure where a first mounting member and a second mounting member are elastically connected by a main rubber elastic body, while a pressure-receiving chamber and an equilibrium chamber are formed in which a non-compressible fluid is sealed on opposite sides of a partition member supported by the second mounting member, and further, an orifice passage is formed to connect said pressure-receiving chamber and equilibrium chamber with each other. For example, the one disclosed in U.S. Pat. No. 6,276,673 is such a device.
In case of a fluid filled vibration damping device with such a conventional structure, the first mounting member is fixed to the smaller-diameter end, which is one end of the main rubber elastic body in an approximate form of a truncated cone, while an insertion metal fitting in a cylindrical shape is fixed onto the outer peripheral face of the larger-diameter end, which is the other end of the main rubber elastic body, and fluid tightness of the pressure-receiving chamber and equilibrium chamber installed therein is secured by means of having the cylindrical portion of the second mounting member bonded by pressure to the insertion metal fitting with a sealing rubber in between in a fluid-tight manner.
Meanwhile, a large tensile load may be applied repeatedly to a fluid filled vibration damping device in a direction of separating the first and second mounting members away from each other, depending on the aspect of how they are mounted. Once such a tensile load is applied, the main rubber elastic body is so much deformed by tension inward in the radial direction that a comparatively large tensile spring force is required for the main rubber elastic body.
However, since the main rubber elastic body is fitted into the second mounting member with the insertion metal fitting in a cylindrical shape in between being fixed onto the outer peripheral face of the larger-diameter end, only the outer periphery of the larger-diameter end of the main rubber elastic body is bound and retained by the insertion metal fitting extending parallel to the input direction of the tensile load. Therefore, when a large tensile load is applied between the first and second mounting members, the inner periphery of the larger-diameter end of the main rubber elastic body is easily pulled and displaced in the direction of the first mounting member (upward), so that required amount of tensile spring force could not be obtained in some cases.
Also considered a problem was a defect wherein the inner periphery of the larger-diameter end of the main rubber elastic body displaced upward by the inputted tensile load collides against the partition member to make striking noises when the end face of the inner periphery is brought back to the initial position by the elastic force upon release of the inputted tensile load.